1. Field of the Invention
The present invention relates to holey graphenes, graphene nanomeshes, holey carbon nanotubes, or holey carbon nanofibers, and, more particularly to holey graphenes, graphene nanomeshes, holey carbon nanotubes, or holey carbon nanofibers formed by controlled catalytic oxidation.
2. Description of Related Art
All references listed in the appended list of references are hereby incorporated by reference, however, as to each of the above, to the extent that such information or statements incorporated by reference might be considered inconsistent with the patenting of this/these invention(s) such statements are expressly not to be considered as made by the applicant(s). The reference numbers in brackets below in the specification refer to the appended list of references.
Graphene sheets are two-dimensional, conjugated carbon structures which are only one or a few atoms thick. They are currently among the most studied nanomaterials for potential applications in electronics, energy harvesting, conversion, and storage, polymer composites, and others.1-4 Graphene sheets with the most ideal structures are experimentally obtained via mechanical exfoliation (the “Scotch Tape” method), which only produces very small quantities.1 For the bulk preparation of graphene, one of the most popular methods usually starts with strong oxidation of natural graphite into graphene oxide (GO) that is dispersible in aqueous solutions as an exfoliated monolayer or few-layered sheets.3 The exfoliated GO sheets may then be chemically or thermally converted into graphene—or more accurately “reduced graphene oxide” (rGO). Compared to the graphene sheets prepared from mechanical exfoliation or chemical vapor deposition methods, chemically exfoliated rGO sheets usually have more defects.3,5,6
Nevertheless, graphene sheets prepared from any method always contain intrinsic defects. Typical types of defects on graphene surface are Stone-Wales (pentagon-heptagon pairs) or vacancy sites, which are mostly of nanometer sizes.5,6 Recently, there have been a few reports on novel types of graphene structures which are featured with large pore openings (i.e., holes) on the conjugated carbon surface.7-18 Compared to conventionally termed defects that often take extensive efforts to observe using high-resolution microscopic techniques,5 the pore openings in these novel holey graphene (hG) structures are much larger (ranging from a few to hundreds of nanometers) and are thus easily identified. The hG structures obtained from lithographic methods, often referred to as “graphene nanomeshes”, usually had spherical hole geometry with controlled sizes.7-14 For example, Bai et al. took advantage of phase-segregated domains of polystyrene-poly(methyl methacrylate) diblock copolymers and used them as the starting templates for the lithographic preparation of secondary SiO2 nanomesh masks via reactive ion etching.7 The porous SiO2 mask, on top of a graphene flake, was then placed under oxygen plasma for the removal of exposed carbon atoms underneath. This resulted in supported or free-standing (upon lift-off) graphene nanomeshes with spherical holes of a few to tens of nm in diameter with various periodicities.
In another example, Liang et al. reported a very similar lithographic process but with the use of a porous polystyrene resist layer obtained with the use of an imprint template.9 The periodic holes on the graphene nanomeshes induced interesting tunable semiconducting properties that may result in transistor devices for unique electronic applications.
A great obstacle for the nearly perfectly structured “graphene nanomeshes” in applications beyond electronics is that they can be only prepared on a substrate-level and are not readily scalable. Alternatively, hGs could be obtained from oxidative methods in larger quantities, despite somewhat less controlled hole geometries, periodicities and size distributions than the graphene nanomeshes.15-18 For example, Kung and coworkers reported that the sonication of an aqueous mixture of dispersed GO and concentrated nitric acid resulted in GO sheets (and upon reduction, rGO sheets) with holes of various sizes.15,16 Such hG films obtained via filtration showed high performance in lithium ion storage, which was attributed to enhanced ion diffusion channels due to the holes on the graphitic surface. In another report, Star and coworkers found that a mild enzyme treatment using horseradish peroxidase could catalyze the oxidation of GO, resulting in holey GO sheets with hole sizes gradually increased over the course of the reactions (up to a few weeks).17 It was interesting that the same enzyme treatment was ineffective toward rGO, which were attributed to less dynamic enzyme functions.
It is a primary aim of the present invention to provide carbon allotropes or graphene nanomeshes.
It is an object of the invention to provide carbon allotropes formed by controlled catalytic oxidation.
It is an object of the invention to provide carbon allotropes in scalable quantities.
It is an object of the invention to provide carbon allotropes with minimal defects.
It is an object of the invention to provide a facile and well controllable method for preparing carbon allotrope structures, which contain holes on the surfaces etched via catalytic oxidation of graphitic carbon by deposited metallic nanoparticles, such as silver (Ag), gold (Au), or platinum (Pt) nanoparticles, or metallic oxide nanoparticles, or combinations thereof.
It is a further object of the invention to provide a method for preparing carbon allotrope structures which has controlled hole sizes on the graphitic surface.
It is a further object of the invention to provide a method for preparing carbon allotrope structures which is readily scalable.
Finally, it is an object of the present invention to accomplish the foregoing objectives in a simple and cost effective manner.
The above and further objects, details and advantages of the invention will become apparent from the following detailed description, when read in conjunction with the accompanying drawings.